1. Field of the Invention
This invention generally relates to cable conduit devices, and more particularly to a fire-rated feed-through fitting for transferring insulated wires through a concrete floor of a building by which electrical power and other signals, such as telecommunications signals, are transmitted from a source located at one face of the floor through an opening in the foor and to respective receptacles mounted on the opposite face of the floor.
2. Description of the Prior Art
Modern office buildings are typically multi-floor structures in which each floor is formed of a concrete slab. Typically, with this form of structure, it has been customary to transmit power and telecommunications signals from floor to floor through openings provided in each floor for that purpose. Thus, it has been customary to form openings in the concrete floors, to insert a feed-through fitting through the opening, to pass the wires through the feed-through fitting from the opposite face of the floor to the top face of the floor, and to make connection to an electrical outlet mounted over the opening on the top face of the floor. While this technique for wiring a building is perfectly satisfactory from the standpoint of achieving the requisite wiring interconnections throughout the building, nevertheless it has been found that the ability of the building to contain a fire which may have been started on one floor is compromised as a result of the tendency of the fire to spread through the feed-through openings to adjacent floors.
Prior art feed-through fittings have included a head assembly mounted over the floor opening, a conduit secured to the head assembly and inserted in the floor opening, and a bottom face receptacle secured to the conduit and abutting the bottom face of the floor such that the floor is in effect clamped between the head assembly and the bottom face receptacle, thereby maintaining the entire assembly in place. Additionally, it has been known to separate the feed-through conduit into two sections and to dispose between the conduit sections an intumescent barrier which expands upon subjection to heat to block the opening and thereby retard the spread of fire and smoke through the opening. Similarly, intumescent barriers have also been disposed within the conduit itself to likewise prevent the spread of fire and smoke through the conduit. In spite of these precautions, however, it has been found that the heat generated by a fire is often of such intensity that the intumescent barrier is itself incinerated, thereby losing its effectiveness. Furthermore, since the conduits themselves are formed of a metal, and are typically rigidly secured to the head assembly by bolts, screws or other rigid means, these prior art fittings serve as an excellent thermal conductor of heat between floors, thereby aggravating the fire containment problem.
Another problem associated with the prior art feed-through devices involves the actual connection of the wires fed through the feed-through assembly to the receptacles mounted on the head assembly. Typically, in order for the workmen to have enough wire to work with during connection of the wire through the receptacles, it is necessary to draw through the opening sufficient slack wire with which to work during the actual making of the electrical interconnection. Prior art feed-through fittings have not provided adequate space between the head assembly and the feed-through conduit for storage of excess slack wire, resulting in squeezing of the slack wire between the head assembly and the conduit, and potential puncture of the wire insulation.
A further problem associated with prior art feed-through fittings resides in the mounting techniques by which the fitting is retained in place in the floor opening. This problem is particularly acute in the mounting of feed-through fittings through floors having a corrugated bottom face, as is commonly found in modern buildings. In that event, it has been found that the surface of the bottom face receptacle is often mounted at an angle with respect to the transverse plane of the concrete floor, thereby resulting in transverse stresses in the means used to secure the bottom face receptacle, which can often lead to an unacceptably loose or unstable feed-through mounting.
Typical feed-through insertion fittings of the prior art are disclosed in U.S. Pat. Nos. 3,751,576; 3,803,341; 3,864,883; 3,995,102; and 4,099,020. See also Abrams et al, "Fire Tests of Poke-Through Assemblies", Fire Journal, May 1971, pp. 56-67 for an overview of the prior art.